Methods: Rados-60R with an energy compensated PIN diode and the SAIC Pd-10i with a miniature energy compensated Geiger-Muller tube EPDs were characterized. The experimental setup and calculation of EPD energy responses were based on ANSI/HPS N13.11-2009. 15 Rados-60R and 2 SAIC Pd-10i units were irradiated using 99mTc, 131I, and 18F radionuclides corresponding to emission energies at 140 keV, 364 keV, and 511 keV, respectively. EPDs output in Hp(10) [mrem] were recorded for free-in-air and with 15-in. thick PMMA to simulate backscatter form the torso. Simultaneous exposure rate measurements were also performed using 2 Victoreen 451-B ionization survey meters to serve as gold standard measurements. The expected EPD Hp(10) values were calculated from exposure (from the Victoreen 451-B survey meters) to Hp(10) as specified in ANSI/HPS N13.11-2009 and ICRU Report 57. These measurements were repeated for both setups at all energies.

Results: On average, in the presence of acrylic, the reported Rados-60R values increased by 27%, 12%, and 13% and those reported by the SAIC Pd-10i increased by 23%, 19%, and 12% at 140 keV, 364 keV, and 511 keV, respectively. The Rados-60R EPDs were observed to under-respond at 140 keV by ~16%, and agreed to within 5% and 10% of the expected values at 364 and 511 keV, respectively. The SAIC Pd-10i EPDs were observed to over-respond at 140 keV by ~20%, and agreed to within 5% of the expected values 364 and 511 keV.

Conclusion: Both Rados-60R and SAICPD-10i EPDs displayed Hp(10) values that were accurate to within 10% at energies above 364 keV. However, their accuracies degraded to 15-20% at lower energies (140 keV) suggesting the need to calculate energy dependent correction factors.